Method of manufacturing spark plug shell and ground electrode assemblies



fii 2,712,685

Patented July 12, 1955 United States atent 2 Fig. 7 is a fragmentary side elevational view with an electrode element assembled in the shell as in Fig. 6.

27126S5 Fig. 8 is a perspective view of the plug shell and ground DIETHOD {3F MANUFACTURING SPARK PLUG electrode assembly after the electrodes have been welded SHELL AND GRQUND ELECTRODE AS- to the shell. SEMBLIES Fig. 9 is an enlarged fragmentary view on a line corre- Stepheu I. Johnson, Rex J. L. Dutterer, and Anthony J. Sponding line of 8 showing the electrode Hein, Hastings, Mich, assignors to Hastings Manuanda port on of its welded connection to the shell. facturlng Company, Hastings, Mich. Fig. is a detailed fragmentary view on a line corl0 responding to line 1010 of Fig. 9 showing further details Apphcatwn August 1951,5313} 240,586 of the welded connections for the ground electrodes to 4 1 m (CL 5 1 the shell and their relation thereto.

It should be understood that all of these views are considerably enlarged, this being done in the interest of clear- Thl's inVeBtiOll relates t0 impffillemems 1T1 method 0f 5 ness and convenience in illustration; however, spark plugs manufacturing spark plug shell and ground electrode are d i djff m 1' e3 assemblies. In Fig. l we illustrate a complete spark plug embodying This application is a Continuation in P of our PP a shell and ground electrode assembly produced by our cation for Letters Patent filed April 28, 1950, for Method th d, The spark plug comprises the shell designated 0f Manufacturing spark Plugs, Which application Was 11 by the numeral 1 and having a pair of ground electrodes division of our application for Letters Patent filed August 2 Th insulator 3 i d d to receive th h ll, th

1949, Serial 107,376, Paffiflt 2,514,543, issued insulated electrode 4 being carried and insulated by the October 21, 1952, for Spark Plugs and Method of Making i l t Spark Plugs. In the practice of our method the shell 1 is desirably The main objects of this invention are! formed on a screw machine. The shell is provided with a First, to provide a method f manufacturing p k p g cylindrical inner portion 5 shouldered at 6 to provide the shell and filCCllOdfi assemblies which when assembled in end edge portion 7 of reduced diameter, Opposed pairs a spark plug maintain their efficiency during long periods f lot 3 are th milled or out through th i e e d of time. edge of the shell. The planes of these slots are parallel Second. to provide a method f f ring p k and laterally spaced on opposite sides and in laterally plug shell and ground electrode assemblies which are well spaced relation to the axial center of the shell. The posiadapted for so-called heavy duty use and use under tioning of these slots with their planes in parallel spaced severe working conditions, one in which the electrodes are relation and in spaced relation to the axial center of the efiectively protected against erosion and against accidental shell is clearly shown in Fig. 3. After the slots 8 are cut, injury i handling, both in the assembly with other parts the inner end of the shell is counterbored as shown at 9 of a spark plug and in use, and one in which the ground in Fig. 4.

electrodes can be easily and quickly gapped or adjusted In Fig. 5 we illustrate one of the electrode elements 10 without the aid of special tools and without likelihood which are of flat section and have rounded edges 11. of breaking the electrodes. These electrode elements are inserted in diagonally oppo- Third, to provide a method of producing spark plug site slots 8 and are preferably fitted into the slots with shell and ground electrode assemblies in which the likelisome pressure with the bottom curved edges thereof resthood of becoming excessively or injuriously heated in ing on the bottoms of the slots as shown in Fig. 7. The use is minimized and one in which there is an efiective inner ends of the electrode elements are spaced from the current and heat transfer joint between the shell and the opposite slots of the pairs and their inner ends are in electrodes. laterally spaced overlapping relation. The next step is Fourth, to provide a method having these several to weld the electrodes to the shell. This is done by simuladvantages which enables rapid and economical productaneously applying welding current and pressure which tion with great uniformity. results in a welded joint indicated at 12 in Figs. 9 and Objects relating to details and economies of the method 10, the weld being on both the bottom and sides of the will appear from the description to follow. The inven- 5O electrodes. tion is defined and pointed out in the claims. It will be noted that the width of the electrode elements A completed spark plug comprising our invention and it) exceeds the depth of the slots 8 and when the electrodes a complete shell and ground electrode assembly and cerare heated they are pressed into the slots, forming a very lain of the steps in producing the same are illustrated in efiective heat and electrical transfer contact with the walls the accompanying drawing, in which: of the slots The inner portions of the electrode elements Fig. 1 is a perspective view of a spark plug embodying are pressed into the counterbore 9 as indicated at 13 in the shell and ground electrode assemblies produced by Fig. 9. our method. After the electrodes are welded into the shell, the inner Fig. 2 is an enlarged fragmentary perspective view illus end of the shell is externally machined or hollow milled trating one of the steps and certain details of the shell as to remove any projecting ends of the electrodes and to produced on a screw machine. chew up any distortions which may result from the weld- Pig. 3 is an inner end View, the inner end only of the ing operation. The threads 14 are then formed on the shell being shown with pairs of slots milled or cut therein. cylindrical portion 5 of the shell, preferably by a rolling Fig. 4 is a fragmentary perspective View corresponding operation. The rolling of the thread extending across the to that of Fig. 2 with the slots milled in the inner end of outer ends of the electrodes further acts to hold them the shell. in place.

Fig. 5 is a perspective view of the blank or piece of The curved or rounded edge 11 is a feature of advanground electrode element stock. tage, particularly in resistance welding. We desire to Fig. 6 is a fragmentary perspective view corresponding point out, however, that there are other types of welding generally to that of Fig. 4 with a pair of the electrodes such, for example, as the condenser capacity discharges inserted in a diagonally opposed pair of slots preparatory which are not so dependent upon the resistance between 7 to the welding step. the two elements being welded together. The counterbore welding and it is of further advantage in that it provides more space in which to move the electrodes for adjustment permitting a relatively large amount of gases in the combustion chamber to circulate around the sparking point and thereby serves to secure better and more positive firing.

The opposed slots are open to permit adjustment of the free inner ends of the electrode as by means of a screw driver engaged in the open slot aligned with the electrode to be adjusted. This permits the accurate adjustmentto and from the insulated electrode 4. In addition to this feature of advantage in adjustment, the edges of the open slots form reaming edges for cleaning the threads of the plug receiving bore of the combustion chamber.

Our method has the further advantage in that it enables large quantity production with uniformity of products. The ground electrodes lie within the shell and are protected to a very substantial extent from the flame flow across the inner end of the plug and consequent erosion.

The spark plug shell and ground electrode assemblies produced by our method are highly efficient and highly durable in use. We have illustrated the steps of our method which we believe will enable those skilled in the art to practice the same in a practical manner.

Having thus described our invention, what we claim as new and desire to secure by Letters Patent is:

I l. The method of making spark plug shell and ground electrode assemblies comprising the steps or" forming a tubular metal spark plug shell, cutting opposed pairs of aligned slots through the inner end edge thereof with the planes of the pairs of slots parallel and laterally spaced and on opposite sides or" and in laterally spaced relation to the axial center of the shell, pressure inserting electrode elements of fiat section and having a rounded edge edgewise into diagonally opposite slots with their rounded edges contacting the bottoms of the slots and with their inner ends in spaced relation to the opposed aligned slot and proiecting beyond and in laterally outward spaced relation to the axial center of the shell, applying pressure to the outer edges of the electrode elements and simul' taneously therewith applying welding current to produce a weldedheat and current conducting joint between the electrode elements and the shell with the electrode'elemerits lying within the plane of the inner endof the shell, the axially inner edges of the electrode elements being deformed by said pressure axially inwardly of the shell along the radially inner ends of the slots in which they are received into heat conducting contact with the inner surface of the shell.

2. The method of making spark plug shell and ground 3 electrode assemblies comprising the steps of forming a tubular metal spark plug shell with a generally cylindrical inner portion, cutting opposed pairs of aligned slots through the inner end edge thereof with the planes of the pairs of slots parallel and laterally spaced and on opposite sides of and in laterally spaced relation to the axial center of the shell, inserting electrode elements into diagonally opposite slots with their inner ends in spaced relation to the opposed aligned slot and in laterally outward spaced relation to the axial center of the shell, applying pressure to the electrode elements and simultaneously therewith applying welding current to produce a welded heat and current conducting joint between the electrode elements and the shell with the electrode elements lying within the plane of the inner end of the shell, and threading the said cylindrical portion of the shell.

3. The method of making spark plug shell and ground electrode assemblies comprising the steps of forming a tubular metal spark plug shell, cutting opposed pairs of aligned slots through the inner end edge thereof with the planes or the pairs of slots parallel and laterally spaced and on opposite sidesof and in laterally spaced relation to the axial center of the shell, inserting electrode elements into diagonally opposite slots with their inner ends in spaced relation to the opposed aligned slot and in laterally outward spaced relation to the axial center of the shell, applying pressure to the electrode elements and simultaneously therewith applying Welding current to produce a welded heat and current conducting joint between the electrode elements and the shell With the electrode elements lying within the plane of the inner end of the shell, the axially inner edge of the electrode being deformed by said pressure axially inwardly of the shell along the ra'dially inner end of the slot in which it is received into heat conducting contact with the inner surface of the shell.

4. The method of makin spark plug shell and ground electrode assemblies comprising the steps of providing a metal shell, forming opposed pairs of slots in the end edge thereof with the corresponding slots of the pairs in alignment, the aligned slots being in parallel planes and spaced laterally relative to the center of the shell, inserting electrodes in diagonally opposed slots, and welding them into the slots with the electrodes Within the plane of the end of the shell.

References Qited in the file of this patent UNlTED STATES PATENTS 

